Surface propellers that operate partially submerged are a popular means of propelling high-speed boats. These surface propellers are normally mounted aft of the transoms of boats so that they receive inlet water that arrives at the surface propeller more or less level and at the horizontal centerline of the surface propeller. A disadvantage of the prior surface propeller technology is that they extend below the keels of the boat by about one half of the propeller diameter. They are subject to high structural shock loads caused when the surface propeller blades impact the water surface on each revolution. Further, these surface propellers must be made as thin as possible in construction to enhance efficiency which results in a highly stressed propeller blade design that cannot handle high impacts that occur when the propeller strikes foreign objects. One solution is to raise the surface propeller above the keel of the boat and encase it in a housing as has been demonstrated in Applicant's Hydro-Air Drive inventions.
The instant invention is a variation of the Hydro-Air Drive. It has application to all manner of boats but has particular application to multi-hulled boats such as catamarans. In the case of application to multi-hulled boats, the fluid accelerating rotor is located on the inboard sides of the hulls so that it does not extend outboard of the beam of the boat. When installed on the outboard sides of hulls of monohull or multi-hulled boats, the beam must be increased. The rotors or propellers are raised such that their lower peripheries are normally higher than a keel of the boat to insure shallow draft capabilities. On relatively small vessels, say up to about 100 feet in length, the rotor is operating with at least some of its inlet water from the waves generated by the bow and other portions of the hull forward of the rotor. Since the water level generated by these bow waves is above the ambient sea level, it is possible to operate with the stated raised rotor. On larger vessels the aft end of the hulls may be submerged deep enough so that less disturbed water is taken in by the instant invention's fluid accelerating rotor. In any case, the instant invention boat propulsion system makes for a simple propulsor with an elevated rotor thereby providing a very shallow draft multi-hulled or monohull boat.